1. Field of the Invention
This invention relates generally to positive drive stepless transmissions, and more particularly concerns a variable speed transmission apparatus having energy transferring means extending interactively between rotating driving and driven members.
2. Description of the Prior Art
Positive drive stepless transmissions have earlier been disclosed in U.S. Pat. Nos. 4,367,067; 4,650,445; 4,676,768; 4,692,128; 4,798,567; 4,820,242 and elsewhere. In general, such transmission devices are characterized in having a rotating drive member and a rotatable driven member having a tapered or conical surface. The axles of both the drive and driven members are in a parallel spaced apart relationship. An endless loop compliant energy transfer means such as an inextensible transmission belt or chain extends between said drive and driven members in tight frictional engagement therewith. A shifting device is provided which can move the belt or chain along the conical surface of the driven member. When the chain is positioned to act upon that portion of the conical surface having smallest circular diameter, the driven member will rotate at relatively high speed, whereas when the chain acts upon that portion of the conical surface having larger effective circular diameter, the driven member will be caused to rotate at a relatively low speed.
Difficulties have been encountered in shifting the transmission belt or chain, especially at the stopped state and at low speeds of operation. The apparatus of U.S. Pat. No. 4,367,067 seeks to overcome such shifting difficulty by employing a transmission chain equipped with laterally moveable ball bearings that interact with undulating surfaces within V-shaped grooves in drive and driven sheaves.
Other difficulties encountered in continuously variable transmissions include poor efficiency with which the transmission belt or chain interacts with the conical surface of the driven member, and rapid wear of component parts, especially the conical surface. Complexity of construction has been another obstacle to the more widespread use of such transmission devices, especially in bicycles.
It is accordingly an object of the present invention to provide a continuously variable stepless transmission device having improved operation at low and zero speeds.
It is another object of this invention to provide a transmission device as in the foregoing object having an endless transmission means which achieves improved driving contact with a conical driven member.
It is a further object of the present invention to provide a transmission device of the aforesaid nature of simple construction amenable to low cost manufacture.
These objects and other objects and advantages of the invention will be apparent from the following description.